Cross connectors are known to provide transverse rigidity to a dual rod spinal stabilization in a patient. Cross connectors are typically fastened to two parallel connecting rods spanning a length of the spine on opposite contralateral sides of the median plane of the spine. Cross connectors in general can be clumsy to place on the rods in a rod/screw construct, a difficulty that is enhanced by the limited ability to manipulate or position the typical cross connector. For instance, certain cross connectors only permit relative movement of rod-engaging ends towards or apart from each other. In some cases the cross connector may permit relative rotation between the rod-engaging ends within a single plane parallel to the axis of the cross connector. Other cross connector designs allow rotation of a rod-engaging end about its own longitudinal axis.
One known version of a cross connector is used to connect the ends of the cross connector to a portion of the longitudinal connecting rods extending between bone anchors, such as hooks or pedicle screws. An example of this type of cross connector is shown and described in commonly assigned U.S. Pat. No. 8,372,120, entitled “Multi-axial Cross Connector”, issued on Feb. 12, 2013 to Anthony James (the '120 patent), the entire contents of which are incorporated herein by reference.
Another type of known cross connector is used to attach to the longitudinal rods at the location where such rods are joined to the bone anchors. This type of cross connector is often considered when the space between bone anchors and hence the extent of the longitudinal connecting rod therebetween is minimal. This condition tends to occur in the cervical spine where vertebrae are smaller than the thoracic or lumber regions of the spine and space for spinal fixations systems is limited. Examples of this type of head to head cross connector are shown and described in U.S. Pat. No. 5,397,363, entitled “Spinal Stabilization Implant System”, issued on Mar. 14, 1995 to Gelbard, and U.S. Pat. No. 6,592,585, entitled “Spine Fixing System”, issued on Jul. 15, 2003 to Lee et al. Adjustability of these cross connectors is somewhat limited
As these systems have evolved, various degrees of freedom of relative orientation were integrated into the systems in order to accommodate misaligned spinal curvature as well as to more flexibility adjust to space limitations as well as anatomic conditions. Advances in head to head cross connectors with improved flexibility and adjustability are shown and described in U.S. Pat. No. 8,672,978, entitled “Transverse Connector”, issued on Mar. 18, 2014 to Dant et al., and U.S. Pat. No. 8,784,452, entitled “Transconnector” issued on Jul. 22, 2014 to Saidha et al. While showing improvement in flexibility and adjustability, a drawback of these cross connectors is the increase in height profile at the location of the connection to the bone anchor
Nevertheless, there is a need for a head to head cross connector that provides enhanced degrees of freedom to address the wide range of spinal treatment protocols that may be encountered, as well as to provide a relatively low profile at the juncture of the cross connector, bone anchor and connecting rod is a spinal stabilization system.